Apparatus for clarifying and purifying liquids



Nov. 19, 1946. l H. c. PARKER ETAL 2,41I,386

APPARATUS FOR CLARIFYING` AND PURIFYING LIQUIDS Filed Feb. 3, 1943 2SheeS-Sht Y1v Nov. 19, 1946. H. c.` PARKER ETYAL 2,411,386

APPRTTUSFOR CLARIFYING AND PURIFYING LIQUIDS Filed Feb'. 3.l 1943 2Sheets-Sheet 2 '4W/OM@ Patented Nov. 19, 1946 APPARATUS FOR CLARIFYINGAND PURIFYING LIQUIDS Henry C. Parker, Washington, D. C., and Frank D.Prager, Chicago, Hl., assignors to Graver Tank & Mfg. Co., Inc., acorporation of Dela- Ware Application February 3, 1943, Serial No. @564This invention relates to apparatus for clarifying and purifyingliquids.

It isya primary object of our invention to provide an improvedcombination of mixing and clarifying means, in a single tank.

A particular object is, to provide mixing means in a loweror mixingcompartment of the tank, to separate an upper or clarificationcompartment from said lower one by a substantially horizontal tray, toarrange for a liquid circulation in and between said compartments, 'toenforce suitable flow velocities for rapid clarification in said uppercompartment, by stilling baffles, said stilling bailles being installedbetween said compartments, and to -suitably and separately removetreated liquid and separated solids `from the tank. Y

A still more particular object is to utilize said stilling bames as astructural support of the horizontal tray, and of other parts.

A general object is to provide simplicity and economy, with a highdegree of eiliciency. Simplicity and economy are attained by the designwherein a substantially horizontal tray separates the lower mixingcompartment from the upper clarification compartment, with a recyclingdevice centrally arranged. While this design is basically known to theart, we have discovered an improvement thereon, materially increasingits emciency while not sacrificing its basic advantages. We found that,for best results, we require substantial agitation in the mixingcompartment below this tray, and that this agitation must be reduced toa large extent before the liquid enters the upper or claricationcompartment, on each ofthe recycling flows. While a positive recyclingnow is required above the tray as well as below it, we provide for muchgreater velocities thereof in the lower compartment. For

this purpose we install substantially vertical, radial stilling baillesin the annular, peripheral space between the superposed compartments. Asa result we can safely provide a liquid agitation by rapid, horizontalrotation beneath the tray,

without adverse effect on the sludge-clear liquor interface above thetray. Of course, stilling baies are well-known in other combinations,but we believe we are the rst to discover the useful function thereof inthe present combination,

where such bales are arranged in the peripheral space as mentioned.

Our invention can be explained in greater detail by reference to theaccompanying drawings which show, more or less diagrtieally, sevsclaims. (ci. artre) eral embodiments of apparatus within our invention.In this showing,

Fig. l -is a, vertical cross section through one of our clariers,

Fig. 2 is a partial horizontal section, taken along the line 2--2 ofFig. l, q

Eig. 3 is a vertical section through a modication of our clarifier,

Fig. 4 is a partial horizontal section, showing the mounting of thesludge collector, taken along the line 6--'6 of Fig. 3,

Fig. 5 is a vertical section through another modiiication of ourclariier, while Fig. 6 is a plan View of the clarifier of Fig. 5.

In the various figures of the drawings, like parts are indicated by likereference numerals.

Many of the structural elements are common to. all embodiments shown inthe figures. Referring rst to Figs. 1 and 2, a cylindrical tank is showngenerally at I. A substantially flat, circular false bottom or tray 2 ishorizontally and concentrically installed in said tank and scrapers 3are provided operating on the tray. The mixing zone or compartmentbeneath the tray is indicated 'at 4 and the clarifying zone orcompartment above the tray at 5.

A raw water inlet is shown at 8 with a chemical inlet pipe vat 9, bothbelow the tray. The sludge draw-off is indicated at I0, while Vthe clearliquor draw-oil is shown at II at,the top or the tank. i y

It will be noted that this tank is. provided with a preliminary mixingzone 6 which is in the form of a sump and into which the raw liquor,mixed with chemicals, is introduced tangentially.

'I'he tray 2 is slightly spaced from the wall of the tank; and it has acentral opening or recycler I5, whereby there is formed a continuous,annular, peripheral opening or flow channel between. the compartments 4and 5 and a central Y opening or flow channel between the samecompartments. In the annular, peripheral channel between the tray andthe tank wall substantially radial, vertical stilling baiiles I3 areprovided. these bailles being secured to the wall of the tank `and tothe tray and supporting the tray. The

scrapers or sweeps 3 operating on top of the tray are preferably adaptedto move the sludge which settles on the tray outwardly towards theperipheral channel or passageway between the tray and the tankwall--this producing an advantageous counter-current now of sludge andliquor-but the Scrapers may b e adapted to scrape the sludge into therecycler.

In the operation of this elarier the chemicals and raw liquor are mixedor agitated in the preliminary mixing zone (sump) with a rotary' turepasses upwardly into the mixing zone 4 beneath the tray where additionalrotary motion is imparted to it by means of steam tangentially injectedthrough pipe 2| andimpelling the liquor` with further, rotary motion.The centrifugal force produced by this rotary motion tends to cause themixture undergoing clarification to pass upwardly through the peripheralchannel between the tray and the tank wall, across the top Yof the trayand back into the mixing zone through the recycler, thisl tendency beingassisted, if desired, by means of steam introduced through an additionalpipe I9 which discharges downwardly, either in or below the recycler,throughan outlet means I8. The rotary motion prevailing in the mixingzone is stilled by the stillingbaflles installed between the zones, sothat the flow is merely upward in the peripheral channel, and inwardover the tray. The upilow in the peripheral channel combined with theagitation and recycling is sumcient to suspend a bed of sludgeextendingthroughout the mixing zone, extending upwardly through theperipheral channel and across the top of the tray to about the levelA-A. The partially flocculated sludge-in the bed abovethe tray as wellas the liquor is thus recycled to be mixed with the raw liquor,

' chemicals and more fully developed sludge in tirely across thehorizontal cross section of the clarier and that the recycling-tends todistribute the upflow through this interface uniformly without theformation of any boil-ups. Sludge set- 4tles on ltop ofthe tray but isscraped ofi by the slow motion of the Scrapers 3 driven by shaft 33. Theheavier particles oi? sludge eventually collect in the'sump 6, finallybeing drawn oil' through pipe I0. The clear liquor ows out of the top ofthe tank, through the draw-oil or launder II.

During the mixing actions which take place in 4 tallization and, owingto the large number of sludge particles 'present and their intimateadrnixture with the raw liquor the insoluble compoundsformed by chemicalreaction crystallize or precipitate on these foci. Supersaturation ofthe liquor with the insoluble compounds is prevented. The sludgeparticles begin to develop, that is, they increase in size by accretionand agglomeration. When fully developed they tend to settle or toseparate by gravity from the liquor. Intimate mixing insures substantialequality of size and of .degree of development of the sludge particlesat all points.

As the liquor rotates below the tray and passes upwardly through thepassage between the tray and the tank the bulk of the Nsludge particlesentrained by the flow have a size such that. the Sl1S` pending action ofthe now is lust greater than the attraction of gravity. But when thesesludge particles, most of which are substantially completely developed,reach the large and relatively quiescent zoneabove the tray, they tendto fall by 'gravity with vless obstruction. We allow sedimentation ofthe full developed particles upon the false bottom or tray. While mostof the particles may be settleable as they enter the clarificationchamberat the periphery thereof,

there is generally a remainder of small and light particles, which arequite difficult to remove from the liquid. It is particularly in view ofsuch very small and light particle that we prefer to maintain a partialsus ion above the false bottom 2 as well as be vw the same, whichpartial suspension desirably includes particles of'intermediate sizeand//Neight as well as the smallest and lightest ones; which are to bebuilt up and removed. On the other hand we prefer to cause and allowprompt sedimentation of the very largest particles, because these areless efcient than the intermediate ones, in aiding the nal developmentof the smaller particles entering the clarication zone. Under theconditions maintained in our clarification zone, there is a certainmaximum size and weight which can be reached by the particles, as arule. The most developed particles are therefore less subject to growthby accretion, and less suitable as a contact material, than theintermediate| ones'.

Thus there are particle suspending, building, and settling actionspresent in our clarification zone and the net result of these actions isthe formation of a sludge bed with a more or less distinct demarkationbetween liquor .containing suspended sludge and clear liquor. This iscalled the `sludge-clear liquor interface. In our clariiier the combinedeect of the upward flow of liquor and the agitation is advantageouslycony trolled in such fashion as to cause this interface to form at apoint somewhat above the level of the tray, as explained previously. Atthis inter-I ditions well understood in this art, including thel type ofimpurities to be removed from the liquor, the kind of chemicals used, ifany, the velocity and temperature of the flow, the size of theparticles, which again depends on the pH and other conditions, and soon. i

The eect ofthe central recycler I5 is highly important in that thedownward circulation pro- L duced by this element causes inward flowsabove the tray. Such inward flows may be of appreciable quantity andvelocity, and in some instances they` may equal or exceed the generalthroughput flow, without disturbing the partial suspension andsedimentation processes described. In

fact, unless excessive recycling rates are applied,

, interface.

uniform the upward flow through this interface, l

clarification is benefited. '.I'he lines of flow of the liquorundergoing clarification, which might otherwise tend to rise almostvertically from the the greater the rate of flow which can be employedwithout producing turbidity in the clear liquor, i. e. the greater thecapacity of the ier.

The structure of the embodiment of Figs. 3 and 4 differs from that ofFigs. l and 2 in that the small sump of this embodiment is not used as apreliminary mixing zone. Substantially radial baffles I3' between thetray andA the tank wall support the tray, which is sloped downwardlytowards its periphery. `The bailles are also shown slightly sloped from'the vertical. A cylindrical baille IB depends from the tray having avertical centerline in common with the tray and being installed betweenthecenter and the periphery clarof the tray; and this, -with the trayhelps to deiine ,A

a preliminary mixing zone, the raw liquor admixed with chemicals beingintroduced tangentially through the pipe 8 into this zone. A recycler lis provided in the center of `the tray and a second cylindrical baffleI1 is mounted slightly below and around the lower end of this recycler,leaving a space there-between for the recycling of the mixture from thepreliminary mixing zone which is drawn into the recycler by the injectoraction of the steam passing through the pipe I9 and distributeddownwardly through the ring i8, within the baille l1. Sludge may bedischarged from the sump through pipe I or may be collected by collectori4 mounted on the side oi the tank and discharged through the pipe 28.

The operation of this modification is very similar to that of Figs. 1and 2. The raw liquorchemical mixture is caused to rotate in thepreliminary mixing zone inside baille i6. Part of this mixture, passes Vdownwardly through the inner baille il the rest passing directly intothe main mixing zone in the lower part of the clarifier. In this mainmixing zone the rotary motion is maintained with the air or steaminjected through pipe 2l, this motion producing sumcient centrifugalforce to induce a iiow of liquor upwardly through the peripheral owchannel between the tray and the tank wall, across the top of the trayand downwardly through the recycler. The level of the sludge bed, inwhich the sludge particles are uniformly distributed, is indicated bythe line A-A. It is seen that partially developed sludge from the bedabove the tray is i recycled to be mixed with more fully developedsludge in the main mixing zone. The Scrapers 3 are adapted to dischargethe sludge deposited on top of the tray into the peripheral flowchannel. The clear liquor is drawn oi through the central launder il.

The embodiment of Figs. 5 and 6 diiers from the previouslydescribedembodiments in the provision of concentric vertical annularbales or partitions mounted in the upper portion of the tank to guidethe circulating liquid into a horizontal direction as it enters theclarification zone, while avoiding objectionable obstructions andsettling surfaces. A partition 36 is so provided which extends from thetop.of the tank downward to a point a short distance above the tray.` Asecond and outer baille 35 may be added, integrally secured to the edgeof the tray and extending from this edge upward to a point below the topof the tank, thereby leaving a sinuous space through which themixture ofraw water and sludge passes on its way to the central clarifying zone.The clarifier is advantageously operated insuch fashion that thesludge-clear liquor interface is maintained at a level slightly abovethe lower edge of the baille 38 as shown at A-A. notary motion 1sproduced beneath the tray by tangential introduction of a raw liquor, A

the velocity of which can be controlled by means of the pump 20. Therotary motion can be increased to any desired extent in the center ofthe mixing chamber by the use of a horizontally rotatable impeller 2|-Mdriven by a motor reducer 2i-A on top of the tank, through a vertical,central shaft 2l-B. t The central sludge collector which is incorporatedin the tray 2 serves also as a recycler of sludge, which can be passedout of the clarier by means of pipe 28 or into the suction of theimpeller 2I-M in the mixing zone through openings 3|. The sweeps 3operating on the tray slowlyv propel precipitated sludge into thecentral collector, being driven by a suitable mechanism 33-A, through adrum 33-B surrounding the central shaft. Special braces 29 are providedat the periphery of the tray, while intermediate-posts 29-A can also beprovided to support part of the weight of the tray. These posts 23-A arelocated around the rotatable impeller 2i-M. This embodiment of -ourclarifier is particularly adapted for use with raw liquors which producea light flocculent sludge and where inward injection of the liquor intoa very quiescent clarifying space, pursuant to thorough agitation atdecreasing rates, is rcquired. If desired baffle 35 can be omitted.

The space between baille 36 and the tank wall serves to still the rotarymotion of the liquor. For this purpose, stilling baiiies l3-A areinstalled substantially radially and vertically in said space; thesebales cooperating to support the tray 2, partition 3'6, and, in somecases, partition 35. The space above the bailes l-A may serve for theaccumulation: of 'scum and other light impuritles.

What we claim is: 1. A tank for liquid clarlcation comprising a at,circular tray concentrically and horizonperipheral ow channel betweensaid compart-V ments, and a central flow channel between saiciVcompartments; impeller means adapted to rapidly rotate the liquid insaid flocculation cornpartment and to recycle liquid from saidocculation compartment through said annular ow channel, over said tray,and back through said central iiow channel; substantially radial andvertical stilling bailies installed in said peripheral flow channel toprevent continued, rapid rotation of said liquid recycled over saidtray, secured to the wall of the tank and to said tray and supporting atleast part of the weight of said tray; sludge scraper means adapted torotate over said tray; means to slow-ly rotate said sludge scrapermeans; inlet means for liquid to be treated and any chemical reagentsrequired, discharging into said occulation compartment; outlet meansgfortreated and clarified liquid adjacent the top of said clarificationcompartment; andV outlet means for settled sludge in'a lower part `ofthe tank.

2. A tank according to claim 1 whereinthe bottom hasa central sump; saidinlet means discharging into said central sump.

3. A tank according to claim 1 comprising an annular .partitiondepending from the edge of upper, central part of the tank below saidtray,

inside said annular partition.

` 4. A tankaccording to claim 1 comprising an annular partitionconcentrically installed in a peripheral part of said clarificationcompartment and extending-from the top of lthe tank installed within therst and extending from they 8 y y I top of the tank downwards toadiacent but above said tray.

6. A tank according to claim 1 wherein said impeller means comprises arotatable member below said tray, a shaft vertically lextending throughthe center of the tank, and means to rotate said shaft; said tankcomprising posts in said flocculation chamber, located around saidrotatable member. and supporting part of the 10 weight of said tray.

HENRY c. PARKER. FRANK D; PRAGER.

